The present invention relates to sensors used to determine if material handling equipment has successfully engaged and retained a handled object, and in particular to sensors of the proximity sensor-type.
Developments in the material handling field have produced a wide variety of material handling equipment that is either partially or wholly automated. This equipment utilizes a wide variety of mechanisms for engaging and retaining the object to be handled, the particular retention mechanism often being dictated by the configuration and type of material to be handled. Conventional material handling equipment may utilize gripping or clamping jaws, or vacuum cups or the like which are mounted on a bracket or arm that is moved into engagement with the handled piece. Although such material handling equipment typically successfully engages and retains the handled object, occasionally such automated devices fail in either retaining the handled object or by retaining more than one object. Although infrequent, such failures can result in failures in subsequent process steps and result in substantial costs for correcting the failure, employee and equipment down time, and material waste.
In order to avoid failures of the type noted above, a variety of sensors have been used in conjunction with material handling devices to determine if the handling device has successfully engaged and retained the handled object. One type of sensor that has been used for this purpose are photoelectric detectors which require a visual path in order to determine the successful retention of an object. A different type of sensor used with such handling devices are proximity sensors. Proximity sensors utilize a magnetic or other electric field in order to determine if an object is proximate to the sensor. In some instances proximity sensors can additionally perform counting functions to determine if too many objects have been retained. Although these proximity sensors function adequately if operated within the sensor parameters, such proximity sensors typically must be positioned very closely adjacent the handled object in order to obtain a correct reading. The tolerances on the positioning of such sensors are very close and often difficult to maintain. Slight variations, such as occur with a mispositioned mounting bracket can result simply through the routine use of the material handling equipment itself. An improper registry of the sensor results in erroneous error signals by the sensor, which may also lead to any of the aforementioned waste and costs.